Western Superconducting Technologies Research Articles

Study on the NbTi/Cu30Ni Superconducting Switch Wire Recently in WST

The superconducting switch wire is a key component in the superconducting magnet. If the superconducting magnet quenches during the operation, the switch will disconnect automatically and avoid the magnet to be damaged. The Cu-30 wt.% Ni alloy was used as matrix to manufacture superconducting switch wires because of its high resistance characteristic. However, because of its high hardness and work hardening characteristics, the risk of wire breakage occurred easily in the cold drawing process. Therefore, the way to solve this problem is one of the difficulties in the preparation of the superconducting switch wire. NbTi/Cu30Ni superconducting switch wires with filaments number of 55 were designed and fabricated by double stacking method, hot extrusion, cold drawing and heat treatment. Then, the NbTi/Cu30Ni superconducting switch wires with the diameter of 0.500 mm, the Cu30Ni/SC of 1.1, and the maximum length of 40.68 km were obtained. Finally, the six insulated NbTi/Cu30Ni wires and one insulated Cu core wire were cabled to the final cable with the diameter of 1.700 mm and the twist pitch of 36 mm. WST has already achieved mass production of NbTi/Cu30Ni superconducting switch wire. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> at 5 T & 4.2 K of the wire is 280.7 A and the line resistance is 2352 mΩ/m. At present, the Western Superconducting Technologies Co., Ltd (WST) superconducting switch wires and cables have been successfully delivered to many different Chinese superconducting magnet manufactures and received good reviews and feedback.

Cryostat for HECRAL Superconducting Magnet

In order to support the normal operation of HECRAL (Hybrid superconducting Electron Cyclotron Resonance ion source with Advance in Lanzhou) superconducting magnet, a cryostat in the form of immersed in liquid helium was designed, which integrated two two-stage GM (Gifford-McMahon) cryocoolers, helium vessel, thermal shield, outer Dewar, suspension structures, service turret, binary current leads, corresponding monitoring and diagnosis system. The 1st cold head of the two-stage cryocoolers were used to cool the thermal shield and HTS (High Temperature Superconducting) current leads. Enough cooling capacity in the temperature region of 4.2K was supplied by the 2nd cold head to condense the saturated helium vapor evaporated by heat load (including static heat load and dynamic heat load), to realize the “0” liquid helium evaporation operation of the superconducting magnet. The corresponding heat load of the designed cryostat was analyzed, and the WST (Western Superconducting Technologies Co., Ltd.) was commissioned to install the cryostat and carried out cryogenic excitation test. The cryostat is now operated in IMP (Institute of Modern Physics, Chinese Academy of Sciences) and all parts of the magnet and cryostat are working normally, which ensures proper operation of the ion source.

Experimental Research of the New Developed High-Jc Nb3Sn Superconducting Strand for 14 T MRI Magnet

The Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) has announced a project to design and manufacture a high field MRI magnet with a 900 mm warm bore and comprised of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn Rutherford cables in 2017. The maximum magnetic induction of magnet system is 14.3 T and magnetic field homogeneity in a spherical volume with 22 cm diameter is better than 0.5 ppm. The high performance Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand is the potential options to use for such high field magnet system. ASIPP cooperates with Western Superconducting Technologies Company (WST) to develop high performance Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand whose critical current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is higher than 2000 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 4.2 K, 12 T. To obtain the actual performance of WST high performance Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand, three short samples are prepared with different non-copper ratio or different heat treatment, the critical current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> or quench current of all sample is measured at different field by the voltage-current (V-I) method, the residual resistivity ratio (RRR) of all sample is also measured. To study the strand whether it will be affected by low field instability, a small coil is built with WST strand, and the experimental result is presented and discussed in this paper.

Multi-scale 3D modelling of a DEMO prototype cable from strand to full-size conductor based on X-ray tomography and image analysis

The design of a superconducting magnet system of a fusion reactor candidate is usually based on the Cable in Conduit Conductor (CICC) concept. CICC consist of complex structures with several hundreds of highly packed, multistage twisted superconductor and copper strands, cooling structures – all wrapped in thin steel foils and jacketed in relatively thick stainless-steel pipes. As recently demonstrated, such complex morphology can be captured by fully 3D X-ray tomography. One of the three alternative winding pack (WP) options for the toroidal field coils of the European DEMO superconducting magnet system as proposed by the Italian ENEA, features a layer-wound WP design adopting a wind-and-react conductor with high aspect ratio rectangular cross section. A multi-physics modelling requiring high accuracy from the strand to the full-size conductor scale was tested on two X-ray tomography systems. For the microstructural integrity analysis of the internal tin one mm diameter Nb3Sn strand, manufactured by Western Superconducting Technologies, a microtomograph with ˜1 μm feature recognition was used. For the full-size conductor (66 x 25 mm2 internal dimensions) a high energy (> 300 kVp) microtomograph with voxel resolution of ˜20 μm was employed. Voids and/or geometrical imperfections were detected, accurately pin-pointed and locally investigated at high resolution before and after heat treatment. Dimensional measurements on the 3D internal structure of the strand showed the small dimensional changes of the strand after the heat treatment. A significant result was the determination of the twist-pitch factor in a purely non-invasive way. The 3D reconstructions of the CICC cables were used to verify the cabling and compaction processes as well as the structural integrity of the strands, wrapping foils and spiral cooling structures. Also, 3D reconstruction of strand trajectories provided a strong input for a multiphysical modelling/interpretation of mechanical–electrical properties of CICC in cryogenic–electromagnetic environments.

Indentation effects on strain sensitivity of critical current for internal-tin Nb3Sn strand

The cable-in-conduit conductor (CICC) technology has been widely used in large scale superconducting magnet. The Short-Twist-Pitch (STP) design was aimed to avoid the conductor degradation during electromagnetic and thermal cycling. But manufacture of STP CICC deforms the cabled strands significantly. Indentations appear on superconducting strands after cabling and compaction. The conductor used for China Fusion Engineering Test Reactor (CFETR) magnet will be subjected to much higher Lorentz force than ITER. The STP CICC will be the first choice for the conductor design, since it showed no observed current sharing temperature Tcs degradation after electromagnetic cycling. In order to estimate the effects of indentation on the superconducting and mechanical properties of Nb3Sn strands, series measurements have been done on an internal-tin (IT) Nb3Sn strand, fabricated by Western Superconducting Technologies Co., Ltd (WST). The strand was artificially indented and cut to several sections for different kinds of measurements, which mainly included the critical current Ic versus axial strain measurements with Pacman device and stress-strain tests. The results show that the indentation has less impact on Ic, but more impact on mechanical performance. The sample preparation, test results and analysis have been described in details.

Heat Treatment and Structure Optimizations of Internal Tin Nb3Sn Superconducting Strands in WST

Western Superconducting Technologies produced approximately 35 tons of Nb 3 Sn strands for international thermonuclear experiment reactor (ITER) Toroidal field coils using the internal tin process. All performances of the strands met the ITER requirement well. The delivery of Nb 3 Sn strands was finished in 2015. At the present, several kinds of Nb 3 Sn strands with different diameters and structures have been developed. In this study, the influence of heat treatment on different strand diameters was investigated. The results showed that extending the heat treatment time was effective for increasing Jc in strands with larger diameters. A new layout of Nb 3 Sn strand with more subelements and gap between the filaments was also fabricated at Western Superconducting Technologies Corporation, Ltd. After a final heat treatment step for 250 h at 650 °C, the critical current density in the non-Cu areas of the improved 1.2 mm diameter strand was 1110 A/mm 2 at 12 T and 4.2 K, which was approximately 10% higher than the ITER strand. The hysteresis loss of the strand can be significantly reduced to 288 mJ/cm 3 at ±3 T and 4.2 K. Approximately 57 kg of this improved strand was contributed to the prototype conductor for the Toroidal field coils of the EURO fusion DEMO.

Study on the Nb3Sn Rutherford Cable for High-Energy Accelerators

This paper studies the development of the Nb 3 Sn Rutherford cable for high-energy accelerators of Western Superconducting Technologies Company Ltd. (WST). In the first stage of cable development of WST, the cable is made of 18 Nb 3 Sn strands with a strand diameter of 0.818 mm. The experiment focuses on the cable parameters (filling factor of 83-91%, and a pitch length of 45-60 mm) to achieve both a minimal critical current degradation of the strand and a good mechanical stability of the cable for coil winding. Furthermore, the cable parameters laws are proposed. After cabling, the J c degradation is smaller than 5% and RRR (273 K/20 K) is more than 200. Last but not least, the results of the critical current degradation, the cabling parameters, and the microstructure of Rutherford Cable are discussed.

Ongoing Efforts at Internal-Tin Nb3Sn Strand With Higher Jcn and Lower Hysteresis Loss

Western Superconducting Technologies Co. Ltd. (WST) has been keeping in the research and development of internal-tin Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand for higher performance level, for the future fusion reactor after ITER. Deformation optimization, Cu splits, and Sn spacers were applied to prepare Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand with higher J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> and lower hysteresis loss, and the effect of these three factors on performance was investigated and discussed. Compared with the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand for ITER, strand distortion was obviously reduced by deformation optimization and J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> was improved, but at the same time hysteresis level was increased. To reduce the level of hysteresis loss, Cu splits were used to replace a few Nb filaments in each subelement. Cu splits could break the bridging Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn filament rings and as a sequence hysteresis loss was dramatically reduced along with the reduction of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> , which is attributed to low reaction degree of Nb filaments in the outermost subelements. Therefore, Sn spacers between the outermost subelements and the Ta barrier were added, and a 37-subelement structure was used to shorten the diffusion path of Sn. The reaction degree of the filaments was enhanced as well as J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> . Finally, it could be concluded that a 37-subelement structure with Cu splits is effective to reduce the level of hysteresis loss and raise the level of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> .

New Progress of Nb3Sn Strand Production for ITER in WST

ITER toroidal field (TF) systems consist of 18 independent coils that are around the torus, whose primary function is to confine the plasma particles. The TF coil conductor is a cable-in-conduit conductor (CICC) made up of superconducting, Nb 3 Sn-based strands mixed with pure copper strands. As the only supplier in China, Western Superconducting Technologies Company, Ltd. (WST) will supply TF Nb 3 Sn strands using internal tin route for ITER, and over 6,000 km of Nb 3 Sn strands have been produced in the past four years. Main performance of Nb 3 Sn strands, including critical current, n value, wire diameter, Cu/non-Cu ratio, hysteresis loss and RRR are reported and analyzed in this paper.

Stability of concentration-related self-interstitial atoms in fusion material tungsten**Project supported by the Fundamental Research Funds for the Central Universities of Ministry of Education of China (Grant Nos. A0920502051411-5 and 2682014ZT30), the Program of International Science and Technology Cooperation, China (Grant No. 2013DFA51050), the National Magnetic Confinement Fusion Science Program, China (Grant Nos. 2011GB112001 and 2013GB110001), the National High Technology Research

Based on the density functional theory, we calculated the structures of the two main possible self-interstitial atoms (SIAs) as well as the migration energy of tungsten (W) atoms. It was found that the difference of the 〈110〉 and 〈111〉 formation energies is 0.05–0.3 eV. Further analysis indicated that the stability of SIAs is closely related to the concentration of the defect. When the concentration of the point defect is high, 〈110〉 SIAs are more likely to exist, 〈111〉 SIAs are the opposite. In addition, the vacancy migration probability and self-recovery zones for these SIAs were researched by making a detailed comparison. The calculation provided a new viewpoint about the stability of point defects for self-interstitial configurations and would benefit the understanding of the control mechanism of defect behavior for this novel fusion material.

Performance optimization of internal tin process multifilamentary Nb3Sn strands

In this study, internal tin process Nb3Sn strands for the International Thermo-nuclear Experimental Reactor are developed in Western Superconducting Technologies. Short cable-in-conduit conductors manufactured with these strands have been qualified. Mass production is accomplished, and all the performances of the strands meet the requirement of ITER project. Besides, more researches on the effect of strand design on critical current density and hysteresis loss for Nb3Sn strands are carried out. It is found that critical current density can be enhanced by reducing filament diameter and increasing Sn content, and hysteresis loss of the strands can be significantly reduced through Cu split adopted in sub-element.

Influence of the heat-treatment conditions, microchemistry, and microstructure on the irreversible strain limit of a selection of Ti-doped internal-tin Nb3Sn ITER wires*

Systematic studies of the intrinsic irreversible strain limit εirr,0, microstructure, and microchemistry were made on several internal-tin Nb3Sn pre-production wires, fabricated for the domestic agencies of the USA and China participating in the International Thermonuclear Experimental Reactor. These wires were produced by Luvata, Oxford Superconducting Technology (OST), and Western Superconducting Technologies (WST), and were intended for the tokamak’s toroidal-field coils. The results of this study show that, for a final heat-treatment at 650 °C to form the A15 phase, both εirr,0 and the de-pinning field Bc2* improved by increasing heat-treatment duration beyond 100 h for the Luvata wires. On the other hand, we saw no improvement in these two parameters as a function of heat-treatment duration in the OST wires. Furthermore, micro-chemical analysis of OST wires revealed that some Nb3Sn filaments have a Sn- and Ti-rich phase at the interface between Cu(Sn) matrix and Nb3Sn in the form of a shell around individual filaments. This phase is far less prominent in the Luvata and WST conductors, and could inhibit diffusion of Sn and Ti into Nb3Sn filaments during the reaction and may potentially be the reason for the lack of noticeable change in Bc2* with heat-treatment duration in the OST wires. The increase of εirr,0 and Bc2* with heat-treatment duration in the Luvata wires and the lack of increase in the OST wires may suggest a possible correlation between εirr,0 and the stoichiometry of the A15 composition. Investigation of the samples’ microstructure revealed only a small number of cracked Nb3Sn filaments despite the significant and permanent degradation of their critical current Ic when subjected to longitudinal tensile strain ε beyond εirr,0. The scarcity of cracks indicate that Ic(ε) measurements are highly sensitive to crack formation in Nb3Sn filaments, especially at low electric-field criteria ≦̸0.1 μV cm−1, even when the sizes of the individual filaments are only few micrometers. All the strands contained substantial Kirkendall porosity, but we found that the quantity and distribution of the Kirkendall voids vary significantly with strand design. Luvata wires have the least porosity, followed by WST wires, and then by OST strands. However, even though the presence of cracks in the Nb3Sn filaments that are in close proximity to Kirkendall voids suggest a correlation between crack initiation and the proximity of the filaments to these voids, the porosity investigation established no definitive relationship between porosity and εirr,0 in the wires studied.

New progress of ITER-PF strand production in WST

ITER Poloidal Field (PF) systems consist of 6 independent coils with different dimensions and require NbTi superconductor and copper strands. Western Superconducting Technologies Co.,Ltd.(WST) will supply PF2-5 NbTi strand for ITER, and over 14,000 km of NbTi strands have been produced in the past two years. Main performance of NbTi strands, including critical current, n value, wire diameter, Cu/non-Cu ratio, hysteresis loss and RRR are reported and analysed in this paper.

Manufacturing of ITER PF5 and CC Sample Conductors

The design of poloidal field (PF) coils and correction coils (CCs) for the International Thermonuclear Experimental Reactor (ITER) relies on the use of 45-kA NbTi cable-in-conduit conductors. All PF5 and CC conductors are produced in China. Research and development programs are needed to acquire knowledge on the behavior of such conductors. Since the conductors are new, full-size copper dummy conductors have been produced in advance for testing the cabling parameters, the definition of the automatic tungsten-inert-gas welding of a seamless jacket section, the elaboration of cable insertion, compaction, etc. Then, two short qualification conductor samples (the PF5 and the CC) are manufactured at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), Hefei, China, with the NbTi advanced strands produced by the Western Superconducting Technologies Company, Ltd. In this paper, the manufacturing procedures for the two PF5 and CC conductor samples are described in detail.

Progress on Internal-Tin Route Nb&lt;sub&gt;3&lt;/sub&gt;Sn Superconducting Strand for ITER in China

Multi-filamentary Nb3Sn strand for ITER has been successfully fabricated by a conventional internal-tin (IT) route at Western Superconducting Technologies, Co. Ltd. All the performances of the IT Nb3Sn strand is able tomeet the ITER specifications. In 2010, one hundred kilograms of IT Nb3Sn strand has been cabled, jacketed and integrated into conductor sample titled with TFCN2 by ASIPP in China and tested in CRPP, Switzerland. After 1200 cycles warm-up and cooling down, Tcs of the TFCN2 Sultan sample at 10.78 T, 4.5 K are 6.35 K for the left leg and 6.37 K for the right leg, respectively, which is larger than the ITER lower limit of 5.7 K. This is the first successful Sultan sample made of Chinese Nb3Sn strand. In 2011, the influence of applied axial strain on critical current (Ic) was investigated using TFCN2 strand in the University of Twente, the Netherland. The irreversible degradation of Ic starts around +0.23% tensile intrinsic strain. The heat treatment influence of the duration at 650 °C on microstructure and performance was also studied. It was found that the fraction of un-reacted Nb after heat treatment is dependent on the position in the cross section. The hysteresis loss increases much faster than Ic when the duration at 650 °C increased.

Study of NbTi Superconducting Strands for JT-60SA Toroidal Field Coils

JT-60SA is a fusion experiment designed to support the operation of ITER and to investigate how best to optimize the operation of fusion power plants that are built after ITER. The toroidal field (TF) coils uses the Cable-in-conduit Conductor (CICC) with NbTi superconducting strands. The TF coils will operate at with 25.7 KA @5.65 T, 4.9 K. Western Superconducting Technologies Co., Ltd. (WST) has studied two types of NbTi superconducting strands for the JA-60SA TF coils. The strands choose the internal CuNi alloy for the internal resistive barrier, which is expected to calibrate and control the inter-strands resistances and to better current distribution between strands in CICC. The strand samples were tested in the range of 4 11 T magnetic field at 4.22 K for critical current, and 5.7 K 6.4 K at 5.65 T for current sharing temperature. This paper presents the results on critical current(Ic), critical current density (Jc), current sharing temperature (Tcs), and hysteresis loss of the strands.

Test Results of a NbTi Wire for the ITER Poloidal Field Magnets: A Validation of the 2-Pinning Components Model

A two-components model has been recently developed, for describing the normalized bulk pinning force curves and the critical current density of NbTi strands over a wider B-T range with respect to conventional single-component models. The model was previously successfully applied to data collected on several NbTi commercial strands, with different size, Cu:nonCu ratio, filament diameter and layout, thus confirming the presence of two different pinning mechanisms in conventionally processed NbTi wires. For a further validation, we have extensively tested a strand recently produced by the Chinese Company Western Superconducting Technologies for the ITER Poloidal Field (PF) magnets PF2 to PF5, and applied the model to these data. In order to take into account the observed non-scaling with temperature of the reduced pinning force curves, the model has been updated, including the observed difference in the temperature dependences of the two components contributing to the overall bulk pinning force. The importance of testing wires over very wide temperature ranges is evidenced, and the good agreement between experimental and fit results validate the proposed formulation, which can be regarded as a reliable tool for the description of NbTi performances, to be used in the design of superconducting magnets. From the phenomenological point of view, it is shown that at low temperatures, the two pinning mechanisms contribute to the bulk pinning force, resulting in a pinning force peaking at a reduced field <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Birr</i> ≅ 0.5. As the temperature increases, the pinning force peak moves to lower fields, indicating that the low field component pinning mechanism becomes dominant.

The results of the second Chinese TF conductor sample

In the framework of the ITER qualification tests the second Chinese sample (CNTF2) was tested in the SULTAN facility. The sample was made of two identical ITER TF type cable-in-conduit conductor sections. Internal Sn strands offered by Western Superconducting Technologies Company (WST) were used for the conductor fabrication. The main characteristics of the conductor and the strand are presented as well as the sample assembly details. The test was performed in accordance with the ITER International Organization specified program. In order to evaluate the conductor performance, the current sharing temperature was measured at specified electromagnetic load cycling steps. Few voltage–current characteristics were measured with the aim of n-value estimation. Before cycling load, both conductor sections of CNTF2 showed different performance, but after 1200 cycles and warmed up and cool down, they showed identical performance: the current sharing temperature ( T cs ) was 6.36 K, which exceeds ITER requirement of 5.7 K.

Investigation of Superconducting Properties of ${\rm Nb}_{3}{\rm Sn}$ Strands by Internal Tin Process for ITER

The multifilamentary Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands with a diameter of 0.82 mm and different local area ratios of Nb to copper (LAR) have been successfully fabricated by an internal tin process in Western Superconducting Technologies Co., Ltd. (WST). The heat treatments have been completed in a vacuum condition. The Critical Current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and hysteresis loss of the strands are measured after different heat treatments according to ITER requirement. The maximum I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is about 285 A (4.22 K, 12 T, 0.1 ¿V/cm) and the hysteresis loss is 290 ~ 410 mJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (4.22 K, ±3 T) per strand unit volume. In this paper, the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and the hysteresis loss of the strands with different LARs and different heat treatments are investigated. It is a reference for fabricating the qualified Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands for ITER project in large scale in WST.

Development of Fine Filament NbTi Superconducting Strands for ITER

The NbTi superconducting wires are used for the Poloidal Field (PF) coil of International Thermonuclear Experimental Reactor (ITER). Western Superconducting Technologies Co., Ltd. (WST) has produced conventional NbTi superconducting strand by single stacking for ITER. The final strands has been heat-treated with different duration. The properties of the NbTi strands meet the requirements to ITER PF strand specification. The diameter of the strand is 0.73 mm and filament diameter is 7.8 . The multifilament composite strand is made up of Nb-Ti filaments embedded in a high purity Cu matrix. This paper presents the results of comparative investigations on critical currents(Ic), critical current density(Jc), AC losses of the strands.